1. Field of the Invention
The present invention relates to an ultrasonic probe for use in an ultrasonic diagnostic apparatus or the like.
2. Description of the Related Art
One type of conventional ultrasonic probe for use in an ultrasonic diagnostic apparatus or the like is known as a linear electronic scanning type ultrasonic probe in which rectangular piezo-electric members are disposed linearly.
This type of ultrasonic probe has, as shown in FIG. 4, a vibrating portion 2 defined by a plurality of piezo-electric vibrators 1 which are disposed linearly, an acoustic absorber 3 provided at the reverse side of the vibrating portion 2, an acoustic matching layer 4 provided at the obverse side of the vibrating portion 2, and an acoustic lens 5 provided on the upper surface of the acoustic matching layer 4, the acoustic lens 5 converging ultrasonic waves generated by the vibrating portion 2 and also the reflected ultrasonic waves from a living body in the direction of the arrow A (i.e., the slicing direction).
As a material for the acoustic lens 5, silicone rubber in which the sound velocity is about 500 m/s lower than that in water has heretofore been employed.
Since the acoustic impedance of silicone rubber is about 0.5 (.times.10.sup.6 kg/ms) smaller than that of a living body, it is general practice to mix a finely-divided inorganic powder with silicone rubber to thereby improve the acoustic impedance.
This conventional practice, however, leads to the followings problems:
(A) Attenuation of the ultrasonic wave passing through the acoustic lens 5 is disadvantageously large. This unfavorable effect of the acoustic lens 5 is particularly remarkable in the case of high-frequency ultrasonic waves.
(B) Since the acoustic lens 5 has a convex configuration with a curvature, the closest to the central portion the larger the attenuation factor of the transmitted ultrasonic wave, which results in a lowering in the acoustic beam converging efficiency.